KABUL, AFGHANISTAN — The posters are printed. The rallies are organized. A televised debate is planned.

Campaign season for Afghanistan’s presidential election kicks off Sunday, and the stakes are high for the 11 candidates vying to succeed President Hamid Karzai and oversee the final chapter in a NATO-led combat mission.

The April 5 vote is a pivotal moment in Afghanistan’s history, its outcome seen as make-or-break for the country’s future and key to the level of foreign involvement here after nearly 13 years of war. Billions of dollars in funds are tied to the government’s holding a free and fair election — the first independent vote organized by Afghanistan without direct foreign assistance.

Amid a surge in violence from the Taliban ahead of the NATO combat troop withdrawal at the end of the year, the poll also will be a crucial test of whether Afghanistan can ensure a stable transition. And the West will be watching the vote as a means of gauging the success of its efforts to foster democracy and bolster security over the past 12 years.

“If the result is so contested that the new government lacks all legitimacy and authority, if the election is so manifestly rigged and corrupt that it destroys the willingness of the U.S. even more than is happening already to go on funding Afghanistan, then indeed you can see the setup that we have created going to pieces,” said Anatol Lieven, a professor in the War Studies Department at King’s College in Britain.

A withdrawal of U.S. funding and support would put the future president in a compromised position, struggling to hold together the armed forces while staving off an emboldened Taliban.

Ziaulhaq Amarkhil, chief electoral officer for the Independent Election Commission, noted the “huge difference” between the coming vote and the previous two presidential elections, in 2009 and 2004: Only Afghans will oversee this one.

“This is a very important election, very crucial election because this is the first time from an elected president we are going to go to another elected president,” he told The Associated Press. “We are fully ready — logistically, operationally as well as from the capacity side, the budget side, the timing side.”

The challenges facing the election apparatus are many: The 2009 election was severely marred by allegations of vote-rigging. Safety and security are major concerns, with the Taliban expected to ratchet up their attacks to sow chaos and disrupt the vote.

Sediq Sediqi, spokesman for Afghanistan’s Interior Ministry, stressed that Afghan Security Forces are “well prepared,” but in a sign of the risks remaining, two campaigners were killed on the eve of the election.

Then there is the challenge posed by Karzai’s mercurial behavior and the risk that a deteriorating security situation could be used to justify postponing the vote.

Karzai has essentially run Afghanistan since the American-led invasion in 2001 drove the Taliban from power. While he is constitutionally barred from seeking a third consecutive term, his presence alone will complicate the run-up to the election.

His refusal to sign a security agreement allowing some American troops to remain here after 2014 has thrown a wrench into U.S.-Afghan relations and put the issue front and center in the campaign. The prospect of having to withdraw all American troops has U.S. officials worried about stability in the region.

While Western officials say all the candidates are in favor of the security agreement, all but one has thus far kept silent — partly because of campaign regulations and partly, it appears, to avoid alienating Karzai. The president has not yet endorsed a candidate and is believed to be keen on wielding influence behind the scenes.

Abdullah Abdullah is the only candidate to publicly support the deal. The former foreign minister was the runner-up to Karzai in the 2009 elections and dropped out just ahead of a runoff vote following allegations of massive fraud in the first round.

Two members of his campaign were shot and killed as they left their office Saturday evening in the western province of Herat, according to campaign spokesman Fazal Sangcharaki.

The lineup of other candidates launching their campaigns Sunday illustrates that patronage and alliances among the elite still form the bedrock of Afghanistan’s politics, where tribal elders and warlords can marshal votes. They include Abdul Rab Rasoul Sayyaf, whose long history as a jihadist and alleged past links to Arab militants make him possibly the most controversial candidate and biggest potential worry to Afghanistan’s international allies.

Sayyaf, who also happens to be an influential Pashtun lawmaker and religious scholar, is running with former energy and water minister Ismail Khan, a Tajik, as one of his two vice presidential picks.

Like many of the candidates, he picked a running mate with broader appeal in an attempt to bridge Afghanistan’s ethnic divides. The country’s population of 31 million is roughly 42 percent Pashtun, 27 percent Tajik, 9 percent Hazara, and 9 percent Uzbek along with other, smaller factions. The Taliban are predominantly Pashtun, and Karzai is also Pashtun.

Ashraf Ghani, a Pashtun former finance minister who oversaw the transition of security from foreign forces to the Afghan army and police, ran and lost in the 2009 elections. He tapped former warlord Gen. Abdul Rashid Dostum — who is thought to control the majority of the Uzbek vote — as one of his two potential vice presidents.

Karzai’s former foreign minister Zalmai Rassoul, a Pashtun, is running with Ahmad Zia Massoud, the brother of Ahmad Shah Massoud, the Northern Alliance commander assassinated in an al-Qaida suicide bombing two days before Sept. 11, 2001. Rassoul is a former national security adviser to the government who has tended to stay out of the limelight — but could up end being a consensus candidate among many political factions in the country.

Rounding out the others tipped to be main contenders is Qayyum Karzai, businessman brother of the president.

While the field of 11 could narrow as the campaign grinds on, there is currently no clear leading contender. None of the candidates is expected to garner the majority needed to avoid a run-off.

Given the amount of time — weeks — it will take to count votes and schedule any run-off, it could be June before Karzai’s successor is known.

That timeline is a worry to some NATO planners who stress the need to know whether their assets are staying or going.

Still, Western officials in Kabul accept the possibility that the signature could come from Karzai’s successor — who in addition to confronting the issue of foreign forces will be forced to weigh the prospect of peace talks with the Taliban.

A negotiated settlement is seen as the only way to bring an end to years of conflict. The Taliban have refused to talk directly with Karzai, saying he is a puppet of the West.

Western officials have expressed hope that a credibly elected new Afghan government — and one able to project security — might convince the insurgency that its future viability rests in coming to the table for peace talks.